1. Field of the Invention
This application relates to an improved automotive liquid cooling system for regulating the operating temperature of an internal combustion engines as and specifically a cooling system control which responds to several engine and cooling system characteristics or parameters and utilizes a coolant pressure powered or servo type valve control.
2. Description of Related Art
The typical automotive cooling system for an internal combustion engine includes a liquid coolant filled radiator and engine "water" jacket, a radiator cap to pressurize the radiator, a coolant pump and a thermostat. Basically, the thermostat is designed to either prohibit coolant flow in the closed mode or to allow coolant flow between the engine or radiator in the open mode. This cooling system has been standard for a great many years and it has proved to be relatively reliable and effective.
In the typical cooling system as described above, the well known thermostat responds directly to coolant temperature changes and uses the expansive forces generated by an enclosed thermally expandable material to open the thermostat. Unfortunately, this expandable material may leak or the thermostat may fail to open for some other reason. When the thermostat does not open, the engine will usually overheat and become inoperative.
In addition to the above described problem with a prior cooling system, the typical expansion type thermostat responds only to one engine related operating condition or parameter, namely the coolant temperature at the engine outlet. It is desirable to provide a cooling system which controls engine temperature in accord with several engine and cooling system conditions or parameters. Consequences of the aforedescribed limitations of this type of cooling system are: somewhat undesirable driveability in certain circumstances, less than optimal combustion chamber temperatures, engine knocking under certain conditions, relatively slow engine warmup, decreased engine efficiency and decreased performance.
There have been previous attempts to overcome problems with the conventional cooling system. In U.S. Pat. Nos. 4,475,485 and 4,537,158, cooling systems utilizing thermostats controlled electrically are disclosed. In the '48 patent, a magnetically driven valve is controlled by a micro computer or electronic control unit (ECU). In the '158 patent, a thermally responsive thermostat is used but additional apparatus is added to adjust the valve opening characteristics. Resultantly, a dual range cooling system is achieved. The U.S. Pat. No. 4,484,541 discloses a cooling system using a thermostat which is powered by vacuum pressure. The U.S. Pat. No. 4,545,333 discloses a cooling system with a vacuum pressure controlled thermostat in which an electronic control regulates vacuum pressure. A radiator bypass is also disclosed.